This invention relates to the treatment of sewage and wastewater, and is more particularly concerned with a wastewater pretreatment arrangement for pretreating household sewage locally before it is discharged into a municipal sewage treatment system.
In most municipalities, households and commercial establishments discharge wastewater into a municipal sewage system, in which a network of sewers carries the liquid and entrained waste matter to a central sewage treatment facility. At that facility, the wastewater is fed to a settling tank or basin where sludge, or solid organic matter, is contacted with either aerobic or anaerobic microorganisms, which digest the sludge and convert it into lower order molecular matter i.e., fermenting the sludge to produce CO.sub.2, H.sub.2 O, other gases, and an inert silt-like solid by-product. The liquid waste is treated to remove ammonia, phosphorus and other dissolved matter before the water is returned into the environment.
Homeowners who are not connected to a municipal sewage treatment system can employ a septic tank to receive the household wastewater and digest sludge from the wastewater. Then the liquid portion is discharged into the soil. Septic systems do not remove nitrogen or ammonia from the effluent. Also, there is no means in the septic tank for automatically removing the accumulated matter that remains from the reduction of sludge. It is therefore necessary periodically to pump the sludge out of septic tanks to prevent them from overfilling and clogging.
Because of population growth in many urban regions, the amount of waste being generated places the municipal sewage treatment facility at full capacity, and in many instances above full capacity. Consequently, overburdened treatment systems must frequently bypass the raw sewage around the facility, and this results in raw contaminated wastewater directly entering lakes and rivers.
Therefore there has been great concern about how to reduce the burden imposed on the municipal sewage treatment facility, but no means have been available to do this. In particular, no suitable pre-treatment device or arrangement has been available to reduce the waste burden at the household before the wastewater enters the municipal sewer system.